1. Field of the invention
The present invention relates to a syringe provided with a mechanism capable of hangaring the needle into itself after completion of injection.
2. Description of the prior art
Syringes are being used in a markedly large number principally in the medical field. In recent years, most syringes are of disposable type made of plastics. They have, before use, a plastic cap hung on the tip of the needle so that needle tip cannot directly touch the finger. After use, the syringes are discarded, either after remounting the cap or removal of the needle tip. In this case, after a syringe has been used after removal of the cap and before it is disposed after remounting of the cap, the needle tip that is still exposed often pricks the finger by mistake. Then, if the patient having received the injection is a carrier of a disease such as hepatitis, the disease infects. Prevention of this type infection has been a great concern among clinicians.
In Western countries, cases of AIDS infected due to the use of syringes have been reported, which breeds serious social unrest. Also in Japan, similar situation may happen in the near future.
Let us consider how such infection occurs. Before a syringe is used, pricking of the finger with the needle can never cause infection of hepatitis or the like, causing a wound though. The problem is during the period between the use of a syringe and its disposal and that between the disposal in a container and completion of final treatment of the syringe, while the syringe is handled by many persons engaged. Infection to clinical personnel can be prevented if the needle is hangared inside the syringe after use so that it will not prick the finger. Further it is important to close the fitting hole for the needle provided on the end of the syringe so that the blood or the like of the patient adhered to the needle tip will not ooze outwardly.
Considerable complexity may be required for a mechanism capable of taking out the needle from inside the syringe upon use without pricking the finger and, at the same time, hangaring the needle into the syringe after use. Few attempts have therefore been made to add this type of mechanism to conventional disposable syringes.
As an example of such attempts, WO/90/06148 discloses a mechanism which combines about 10 pieces of complex-shaped plastic molded articles inside a plastic syringe and utilizes the force of a spring, thereby taking the needle in and out. In this mechanism, when the plunger is pushed upon use, the needle housed inside the syringe springs out through the tip of the syringe and is automatically mounted thereon. Then, after sucking a medicine and injecting it into a patient, the plunger is further pushed, which releases the lock and hangars the needle into the syringe by force of the spring. Further the mechanism does not allow the needle once hangared to come out even if the plunger is pushed again.
In this mechanism, the needle has been bent beforehand, is then deformed to straighten upon use and, after use, assumes its original shape when it is withdrawn. The needle thus bent again cannot comes out again even when the plunger is pressed. However, the degree of deformation cannot be sufficiently large restricted by the entire shape and hence the needle tip tends to come out to cause a danger, when parts fixing the needle shift only slightly. Another disadvantage is difficulty in completely sealing the mechanism part, thereby often allowing the medicine to penetrate thereinto. Furthermore, the mechanism contains a large number of parts and has a complex shape so that its fabrication requires a very careful, skilled adjustment.
In this mechanism, the needle is housed inside the syringe before use. However, since infection of virus or the like can never occur before use, it is not considered necessary to add such a complex mechanism for this purpose.